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From: Jacob Keller <jacob.e.keller@intel.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: TonyWWang-oc@zhaoxin.com, acme@kernel.org,
	alexander.shishkin@linux.intel.com, bp@alien8.de, bp@suse.de,
	hpa@zytor.com, jacob.jun.pan@linux.intel.com,
	jarkko.sakkinen@linux.intel.com, jmattson@google.com,
	jolsa@redhat.com, joro@8bytes.org, kvm@vger.kernel.org,
	lenb@kernel.org, linux-edac@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
	linux-pm@vger.kernel.org, mark.rutland@arm.com, mingo@redhat.com,
	namhyung@kernel.org, pbonzini@redhat.com, peterz@infradead.org,
	rkrcmar@redhat.com, shuah@kernel.org, tglx@linutronix.de,
	tony.luck@intel.com, vkuznets@redhat.com, wanpengli@tencent.com,
	x86@kernel.org
Subject: Re: [PATCH v5 13/19] x86/cpufeatures: Add flag to track whether MSR IA32_FEAT_CTL is configured
Date: Wed, 26 Feb 2020 12:41:09 -0800
Message-ID: <df215c4c-82f0-5b15-57c3-d304fd94ff3b@intel.com> (raw)
In-Reply-To: <a9c4b363-1569-f03e-6155-a869dd186ced@intel.com>

On 2/25/2020 4:58 PM, Jacob Keller wrote:
> On 2/25/2020 4:42 PM, Sean Christopherson wrote>> So there's something
> weird going on. Maybe "boot_cpu_has" in the
>>> vmx_disabled_by_bios is wrong? Hmm.
>>
>> Hmm, perhaps a bug somewhere else is overwriting the cpufeatures bit for
>> X86_FEATURE_VMX.  Let me see if I can reproduce from net-next.
>>
> 
> If you have any further suggestions for debugging, I'm happy to help try
> to figure this out. To my eyes, it looks like somehow bits get reset...
> It's definitely not clear to me how this happens.
> 
> There is the get_cpu_caps call.. but that seems to correctly call
> apply_forced_caps at the end.
> 
> That's all I have time for today.
> 
> Thanks,
> Jake
> 

Hi,

I kept digging into this, and I added a further print to the get_cpu_cap
function.

It looks like get_cpu_cap is being called again *after*
init_ia32_feat_ctl...

Digging further, I discovered this appears to be the call in setup_pku,
which would only be enabled for systems which have X86_FEATURE_PKU
enabled and supported. It's quite likely that test systems may not have
had this feature, hence why it went undetected till now.

Because of the extra get_cpu_cap call, the capabilities are reset. Since
we never use setup_clear_cpu_cap or pass NULL to clear_cpu_cap, the code
that sets the global cpu_caps_cleared bits is not run.

It's not clear to me what the best fix for this is.

Perhaps init_ia32_feat_ctl should be something run during
early_identify_cpu, since it's really checking global status (rdmsr),
and not per-CPU status. And then it could directly operate to call
setup_clear_cpu_cap, which would properly clear the bit globally,
ensuring that apply_forced_caps kicks in?

Or this needs to somehow be run *after* setup_pku? But that doesn't feel
very robust.

Thanks,
Jake

  reply index

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-21  4:44 [PATCH v5 00/19] x86/cpu: Clean up handling of VMX features Sean Christopherson
2019-12-21  4:44 ` [PATCH v5 01/19] x86/msr-index: Clean up bit defines for IA32_FEATURE_CONTROL MSR Sean Christopherson
2019-12-21  4:44 ` [PATCH v5 02/19] selftests: kvm: Replace manual MSR defs with common msr-index.h Sean Christopherson
2019-12-21  4:44 ` [PATCH v5 03/19] tools arch x86: Sync msr-index.h from kernel sources Sean Christopherson
2019-12-21  4:44 ` [PATCH v5 04/19] x86/intel: Initialize IA32_FEAT_CTL MSR at boot Sean Christopherson
2019-12-21  4:44 ` [PATCH v5 05/19] x86/mce: WARN once if IA32_FEAT_CTL MSR is left unlocked Sean Christopherson
2019-12-21  4:45 ` [PATCH v5 06/19] x86/centaur: Use common IA32_FEAT_CTL MSR initialization Sean Christopherson
2019-12-21  4:45 ` [PATCH v5 07/19] x86/zhaoxin: " Sean Christopherson
2019-12-21  4:45 ` [PATCH v5 08/19] x86/cpu: Clear VMX feature flag if VMX is not fully enabled Sean Christopherson
2019-12-21  4:45 ` [PATCH v5 09/19] x86/vmx: Introduce VMX_FEATURES_* Sean Christopherson
2019-12-21  4:45 ` [PATCH v5 10/19] x86/cpu: Detect VMX features on Intel, Centaur and Zhaoxin CPUs Sean Christopherson
2019-12-21  4:45 ` [PATCH v5 11/19] x86/cpu: Print VMX flags in /proc/cpuinfo using VMX_FEATURES_* Sean Christopherson
2019-12-21  4:45 ` [PATCH v5 12/19] x86/cpu: Set synthetic VMX cpufeatures during init_ia32_feat_ctl() Sean Christopherson
2019-12-21  4:45 ` [PATCH v5 13/19] x86/cpufeatures: Add flag to track whether MSR IA32_FEAT_CTL is configured Sean Christopherson
2020-02-25 21:49   ` Jacob Keller
2020-02-25 22:12     ` Sean Christopherson
2020-02-25 22:52       ` Jacob Keller
2020-02-25 23:29         ` Sean Christopherson
2020-02-25 23:35           ` Jacob Keller
2020-02-25 23:54           ` Jacob Keller
2020-02-26  0:41             ` Jacob Keller
2020-02-26  0:42             ` Sean Christopherson
2020-02-26  0:58               ` Jacob Keller
2020-02-26 20:41                 ` Jacob Keller [this message]
2020-02-26 20:57                   ` Sean Christopherson
2020-02-26 21:03                     ` Jacob Keller
2020-02-26 21:25                       ` Sean Christopherson
2020-02-26 21:53                         ` Jacob Keller
2020-02-27  2:12     ` Sean Christopherson
2020-02-27  4:20       ` Huang, Kai
2020-02-27 18:09       ` Jacob Keller
2019-12-21  4:45 ` [PATCH v5 14/19] KVM: VMX: Drop initialization of IA32_FEAT_CTL MSR Sean Christopherson
2019-12-21  4:45 ` [PATCH v5 15/19] KVM: VMX: Use VMX feature flag to query BIOS enabling Sean Christopherson
2019-12-21  4:45 ` [PATCH v5 16/19] KVM: VMX: Check for full VMX support when verifying CPU compatibility Sean Christopherson
2019-12-21  4:45 ` [PATCH v5 17/19] KVM: VMX: Use VMX_FEATURE_* flags to define VMCS control bits Sean Christopherson
2020-01-13 18:32   ` Borislav Petkov
2020-01-13 18:37     ` Sean Christopherson
2020-01-13 18:38       ` Borislav Petkov
2020-01-13 18:42         ` Sean Christopherson
2020-01-13 18:52           ` [PATCH] KVM: VMX: Rename define to CPU_BASED_USE_TSC_OFFSETTING Borislav Petkov
2020-01-13 20:16             ` Sean Christopherson
2020-01-14  9:31               ` Borislav Petkov
2020-01-14 17:27                 ` Sean Christopherson
2019-12-21  4:45 ` [PATCH v5 18/19] perf/x86: Provide stubs of KVM helpers for non-Intel CPUs Sean Christopherson
2019-12-21  4:45 ` [PATCH v5 19/19] KVM: VMX: Allow KVM_INTEL when building for Centaur and/or Zhaoxin CPUs Sean Christopherson

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